228 W. H. Hobbs — Paragensis of Allanite, etc. 





1. 



II. 



Si0 2 



37-63 



37-83 



A1 2 3 



[20-86] difference 



22-63 



Fe 2 3 

 FeO 



I 15-29 J 



15-02 

 0-93 



MnO 



0-31 







CaO 



22-93 



23-27 



M<*0 



0-31 





H^O 



2-23 



2-05 



p 3 "o 5 



0-44 







100-00 101-73 



If we consider the phosphoric oxide as due to inclusions of 

 apatite, and disregard the traces of manganese and magnesia, 

 the analysis corresponds very closely with the formula 2H 2 Ca 4 

 Al 6 Si 6 26 +H 2 Ca 4 Fe 6 Si 6 2 , 



The peculiar intergrowths that have been described are char- 

 acteristic of the Ilchester granite throughout the twenty-five 

 square miles of the section studied.* Colorless inclusions, 

 probably apatite, as well as biotite, are occasionally found in 

 the allanite. With little doubt, the latter is one of the earliest 

 separations from the magma. The origin of the epidote is not 

 so easily settled, but the " stretched " character of the granite 

 is in favor of a metamorphic origin through pressure. Against 

 such a view is the discovery by Professor Williams that the 

 Woodstock granite, which is particularly rich in these inter- 

 growths, shows no evidence of cataclastic action. 



In conclusion I would gratefully acknowledge obligation to 

 my much honored teachers, Professor Williams of the Johns 

 Hopkins University in Baltimore, and Professor H. Rosen- 

 busch of Heidelberg, Germany. 



After the foregoing article left my hands, there was brought 

 to my notice the recent important paper of Lacroix on Pyrox- 

 ene-gneiss and Wernerite Pocks (Contributions a l'etude des 

 gneiss a pyroxene et des roches a wernerite, Bull, de la Soc. 

 francaise de Mineralogie, tome xii, No. 4, April, 1889). 

 The author describes similar epidote-allanite intergrowths in 

 the pyroxene-amphibole gneiss of Finisterre (pp. 138-9, fig. 21); 

 in the pyroxene-wernerite gneiss of the Lower Austrian Wald- 

 viertel (p. 157, pi. I, fig. 6); and in the wernerite gneiss of 

 Odegarden in Norway (p. 210). M. Lacroix has found the 

 same properties to characterize the allanite and epidote of 

 these localities as have been determined for the Ilchester inter- 

 growths, specimens of which he has used for comparison. He 

 considers the epidote primary in all the occurrences described 

 by him (p. 353). 



* I am informed by Prof.' Williams that he has found such epidote-allanite 

 intergrowths to be characteristic of the surrounding Ellicot City and Woodstock 

 granites, but wanting in the Guilford granite which occurs farther to the south. 



